This invention is in the field of ceramic powder extrusion, and relates to a plasticized powder mixture and a method for stiffening the mixture. In particular, this invention relates to a ceramic-forming powder mixture and a method for stiffening the mixture by applying electromagnetic radiation to the extruded material.
A long-standing problem with forming of plastically deformable materials which use liquids as part of the plasticizing system has been the delicate balance which is necessary to maintaining material which is plastic enough to form with relative ease, and creating a body which is self-supporting and is able to be handled upon formation. This is a particular problem with pseudoplastic or thixotropic materials which use a liquid as part of the plasticizer since such a material tends to exhibit lowered viscosity immediately after forming as a result of the effects of “shear-thinning” inherent in any forming operation involving the application of shear stress on the material.
Generally, as the viscosity of the plastically deformable material is lowered, the wet, formed structure or article tends to collapse since it is not completely self-supporting. Conversely as the viscosity of the plastically deformable material is increased to create a self-supporting final extruded body, forming of the material tends to require significantly higher forming pressures which in turn means that it becomes necessary to use heavier equipment, more substantial forming members, and abrasion resistant parts.
With current technology, there is extreme difficulty in forming a thin-walled self-supporting body from a plastically deformable material which can be firmly handled without deforming the body, particularly when liquid is used as part of the material plasticizing system. The solution to this problem generally has been either to form only relatively thick-walled bodies, or to create bodies from materials that can be stiffened by rapid cooling or heating. After a self-supporting body has been formed from a plastically deformable material using liquid as part of a plasticizing system, it has been necessary to dry it to remove the liquid prior to sintering particulate material or to harden the formed material to enable machine handling.
U.S. Pat. No. 5,223,188 discloses a method of stiffening plastically deformable material that has been newly formed into a shaped body. The method includes exposing the material, which includes body-forming matter, polar molecules, and a polymeric agent having a thermal gel point, to electromagnetic radiation within the frequency range 107 to 1013 Hertz. The radiation is applied to effect thermal gelling as the shaped body emerges from an extrusion die.
U.S. Patent Publication No. 2005/0093209 discloses an apparatus and method for stiffening a wet extruded ceramic body for improved handling prior to drying and firing. The ceramic body, for example an extruded honeycomb shape, is formed from a plastically deformable material including inorganic raw materials, and organics, such as a binder having a thermal gel point. As the ceramic body exits the extrusion die it is passed through a microwave energy field to be heated to above the gelling point of the organic binder. The ceramic body then stiffens and can be easily handled without deformation.
Notwithstanding the foregoing, numerous problems remain relating to the forming of wet extruded ceramic bodies in a way that can accurately retain a formed shape through handling and until drying. According, efforts continue toward the development of improved methods by which shape retention in wet extruded ceramic bodies could be more effectively achieved, and most preferably achieved using simplified processes and equipment more compatible with existing manufacturing methods.